Time Travel in the Terminator movie franchise is called Time Displacement, which is made possible in the Terminator movie franchise through the use of the Time Displacement Equipment (TDE), developed by Skynet at some point in time before July 11th, 2029.
As evidenced in each of the movies it appears as though the TDE cannot determine exactly where subjects will be displaced. While it seems that subjects are displaced in the vicinity of their source destination, they have been known to arrive in place of pre-existing objects. Luckily the act of displacement removes whatever was present when the chrono-sphere arrives, destroying it if it is not living organic matter.
As also evidenced in each of the movies, when the TDE is activated a bridge between the source and a shifting destination point is created, with the destination point only creating a chrono-sphere whenever a subject enters the TDE. This explains how Kyle Reese was able to follow the Terminator back in time to May 12th, 1984, and how the T-1000 was able to follow the reprogrammed Terminator back in time to June 8th, 1994.